microsoft/semantic-kernel · error · FunctionExecutionException

Error building the URL for the operation {self.id}: {e!s}

Error message

Error building the URL for the operation {self.id}: {e!s}

What it means

The `build_operation_url` method joins the server URL with the operation path to construct the request URL, wrapped in a try/except. If `urljoin` raises any exception (malformed server URL, path, or argument interpolation result), it is caught and re-raised as this FunctionExecutionException with the original error stringified. This is a catch-all for URL construction failures.

Source

Thrown at python/semantic_kernel/connectors/openapi_plugin/models/rest_api_operation.py:229

                if parameter.is_required:
                    raise FunctionExecutionException(
                        f"No argument is provided for the `{parameter.name}` "
                        f"required parameter of the operation - `{self.id}`."
                    )
                continue

            headers[parameter.name] = str(argument)

        return headers

    def build_operation_url(self, arguments, server_url_override=None, api_host_url=None):
        """Build the URL for the operation."""
        server_url = self.get_server_url(server_url_override, api_host_url, arguments)
        path = self.build_path(self.path, arguments)
        try:
            request_url = urljoin(server_url, path.lstrip("/"))
        except Exception as e:
            raise FunctionExecutionException(f"Error building the URL for the operation {self.id}: {e!s}") from e
        self._ensure_request_target_matches_server(server_url, request_url)
        return request_url

    @staticmethod
    def _ensure_request_target_matches_server(server_url: str, request_url: str) -> None:
        """Verify URL construction did not move the request off the configured server.

        A selected operation path must resolve to a request on the same scheme, host, and port and
        within the server's base path. Otherwise an absolute or authority-changing operation path
        (for example "https://another-host/admin") could redirect a credential-bearing request to an
        unintended target even though it carries no dot-segment. This complements
        `_validate_path_segments` so operation selection, path validation, and request construction
        share one canonical target.
        """
        server = urlparse(server_url)
        request = urlparse(request_url)

        if (request.scheme, request.username, request.password, request.hostname, request.port) != (

View on GitHub (pinned to c028a0c7dc)

Solutions

  1. Inspect the inner exception (`__cause__`) for the specific URL parsing error.
  2. Validate the server URL and all path argument values for valid URL characters before calling.
  3. Ensure the server URL override (if used) is a well-formed absolute URL with a scheme.
  4. URL-encode any path argument values that may contain special characters.

Example fix

// before
await api.call_op(server_url_override="not a url")
// after
await api.call_op(server_url_override="https://api.example.com/")
Defensive patterns

Strategy: try-catch

Validate before calling

from urllib.parse import urljoin, urlparse
def validate_url_construction(server_url: str, path: str):
    if not urlparse(server_url).scheme:
        raise ValueError(f"Server URL has no scheme: {server_url}")
    try:
        urljoin(server_url, path.lstrip('/'))
    except Exception as e:
        raise ValueError(f"URL construction would fail: {e}")

Try / catch

try:
    result = await api.my_operation(**args)
except FunctionExecutionException as e:
    if "Error building the URL" in str(e):
        cause = e.__cause__  # inspect the original URL parsing error
        # validate server_url and path argument values
        ...

Prevention

When it happens

Trigger: The server URL or interpolated operation path is malformed in a way that causes `urljoin` to fail, or an argument value produces an invalid path segment. This is a low-level URL parsing failure during request construction.

Common situations: Server URL override contains invalid characters or scheme. Path template argument values contain characters that break URL parsing. Misconfigured server URL environment variable. Extremely rare under normal conditions since most malformed inputs are caught by earlier validation.

Related errors

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/0823aa80b864d23e. Report an issue: GitHub.